JPH0215604B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a method for manufacturing mechanical structural parts, which is particularly applicable to parts manufactured by cold forging among mechanical structural parts. (Prior art) Conventionally, mechanical structural steels used for cold forging include carbon steel (SC), chrome steel (SCr),
There are chromium molybdenum steels (SCM) and nickel chrome molybdenum steels (SNCM).For example, inexpensive carbon steels are often used in the shafts of automobile steering and drive mechanisms. Cold forging has higher processing accuracy and better material yield than hot forging, so its proportion in forming materials has tended to increase in recent years. Generally, carbon steel subjected to cold forging is subjected to spheroidization heat treatment (SA) in order to spheroidize the cementite and give it high deformability.
processing) is applied. However, in the manufacturing method of machine structural parts using machine structural steel used in conventional cold forging, in order to perform spheroidizing heat treatment,
After soaking for about 1 hour just above the A ₁ transformation point, it is necessary to continue cooling to just below the A ₁ transformation point at a rate of about 10°C/hr. Since it required more than 10 hours, there were problems in that productivity was low and energy consumption was enormous. (Purpose of the Invention) The present invention has been made by focusing on such conventional problems, and does not require long-term heat treatment such as spheroidization heat treatment, and has low deformability during cold forging. It is an object of the present invention to provide a method for manufacturing mechanical structural parts that is expensive and suitable for parts manufactured by cold forging. (Structure of the Invention) The method for manufacturing mechanical structural parts according to the first invention of the present invention includes, in weight%, C: 0.05 to less than 0.2%, Si:
Over 1.5 ~ 3%, Mn: over 1.0 ~ 2%, Cr: 0.3 ~
1.3% as a basic component, and if necessary, one or two of Ni: 2% or less and Mo: 0.5% or less as a hardenability improving element, and also as a grain refining element, if necessary. Al: 0.1% or less, Nb: 0.3
% or less, Ta: 0.3% or less, Ti: 0.3% or less, Zr:
N: 0.1% or less, N: 0.03% or less, and the remainder consists of Fe and impurities, and is cooled from the ferrite-austenite two-phase temperature range with air cooling or a cooling rate higher than that to form fine particles. That is, fine ferrite-pearlite, ferrite-pearlite, more preferably grain size number 6 or higher, particularly preferably grain size 7 or 8 or higher.
A method for manufacturing mechanical structural parts according to a second invention which achieves the same object is characterized in that the parts are manufactured by cold forging using a steel material having a bainite or ferrite-bainite structure. So, C: less than 0.05 to 0.2%, Si:
Over 1.5 ~ 3%, Mn: over 1.0 ~ 2%, Cr: 0.3 ~
1.3% as a basic component, and if necessary, one or two of Ni: 2% or less and Mo: 0.5% or less as a hardenability improving element, and also as a grain refining element, if necessary. Al: 0.1% or less, Nb: 0.3
% or less, Ta: 0.3% or less, Ti: 0.3% or less, Zr:
N: 0.1% or less, N: 0.03% or less, and the remainder consists of Fe and impurities, and when finished rolling in material rolling prior to cold forging, Ar ₁ transformation point ~ Ar ₃ transformation point + 100 By applying a reduction rate of at least 20% in the temperature range of °C and then cooling with air cooling or a higher cooling rate.
Even finer ferrite than the heat-treated material mentioned above.
It is characterized in that it is manufactured by cold forging using a steel material having a pearlite, ferrite-pearlite-bainite, or ferrite-bainite structure with further improved transformation ability. Next, the reason for limiting the composition range (weight %) of the cold forging steel used in the method for manufacturing mechanical structural parts according to the present invention will be explained. C: 0.05% to less than 0.2% C is an effective element for ensuring strength as a mechanical structural component, especially quenching hardness, and the lower limit was set to 0.05% in consideration of strength. Further, in order to stably obtain a sufficiently wide temperature range of the ferrite-austenite two-phase, the upper limit was set to less than 0.2%. Si: Exceeding 1.5% to 3% Si is an effective element for widening the temperature range of the ferrite-austenite two-phase, so it is necessary to add more than 1.5%. Further, although it is an effective element for strengthening the ferrite structure, excessive addition causes an increase in deformation resistance and a decrease in toughness, so the upper limit was set at 3%. Mn: Exceeding 1.0 to 2% Mn is an effective element for deoxidizing and desulfurizing during melting, and is also an effective element for ensuring hardening hardness. and more sufficient deoxidation,
In order to obtain a desulfurization effect and at the same time further improve hardenability, the lower limit was set to exceed 1.0%. but,
Excessive addition will reduce cold forgeability, so
The upper limit was set at 2%. Cr: 0.3 to 1.3% Cr is an effective element for improving hardenability and preventing graphitization, and in order to obtain such effects, the lower limit was set to 0.3%. but,
The upper limit was set at 1.3%, taking into full consideration the decrease in toughness. One or two of Ni: 2% or less, Mo: 0.5% or less Ni and Mo are effective elements to further improve hardenability and strengthen the base during heat treatment after forging. Therefore, it is good to add more to the above basic ingredients if necessary, but if the Ni content is 2%
If the Mo content exceeds 0.5%, the toughness deteriorates, so Ni was set at 2% or less and Mo at 0.5% or less. Al: 0.1% or less, Nb: 0.3% or less, Ta: 0.3% or less, Ti: 0.3% or less, Zr: 0.1% or less, N: 0.03%
One or more of the following Al, Nb, Ta, Ti, Zr, and N are effective elements for refining crystal grains and improving cold deformation through the formation of carbonitrides. Therefore, one or more of these may be added as required. However, when the Al content exceeds 0.1%, the Nb content exceeds 0.3%, and the Ta content exceeds 0.3%,
If the Ti content exceeds 0.3% and the Zr content exceeds 0.1%, the carbonitrides will become coarser, which will reduce the grain refining effect and cause a decrease in cold deformability. , when added, it is necessary to keep the above-mentioned upper limit. In addition, the N content
If it exceeds 0.03%, the integrity of the steel ingot or slab will be damaged by N blowholes, so the upper limit of N was set at 0.03%. In addition, in order to increase cold deformability and improve cold forgeability, [O]: 0.003% or less,
S: It is desirable to regulate it to 0.02% or less as necessary. Then, the steel whose composition has been adjusted in this manner is cooled from the ferrite-austenite two-phase temperature range by air cooling or at a higher rate to form a fine ferrite-pearlite, ferrite-pearlite-bainite, or ferrite-bainite structure. , it is possible to obtain a mechanical structural steel with outstanding cold deformability, which can be used to make constant velocity joint parts such as outer races and housing shafts, and axle parts such as rear spindles and axle shafts into spherical shapes. Machine structural parts can be manufactured by cold forging without heat treatment. In addition, when the steel whose composition has been adjusted as described above is finished rolled in the material rolling process prior to cold forging, the temperature range from Ar ₁ transformation point to Ar ₃ transformation point + 100℃ is at least 100℃.
By applying a reduction rate of 20% or more and then cooling with air cooling or a cooling rate higher than that, a finer ferrite-pearlite, ferrite-pearlite-bainite, or pearlite-bainite structure than the above-mentioned heat-treated material is created. By this, the deformability in cold can be further improved,
A mechanical structural steel with extremely excellent properties can be obtained for cold forging, and by cold forging this mechanical structural steel, mechanical structural parts with excellent properties can be manufactured. Here _, during finish rolling in material rolling prior to cold forging, _at least 20
The reason why we decided to apply a reduction rate of % or more is because even if we roll at a temperature higher than the Ar ₃ transformation point + 100°C, we will not be able to obtain a fine structure and the cold forgeability will not be improved. Furthermore, if rolling is performed at a temperature lower than the Ar ₁ transformation point, the effects of processing remain and cold forgeability similarly decreases, and furthermore, by setting the reduction rate to 20% or more, the fineness of the structure is improved. This is because it is possible to improve the cold forgeability, and a reduction ratio smaller than this has almost no effect. Example 1 Steel having the chemical composition shown in Table 1 was melted and ingot-formed, and a round bar with a diameter of 32 mm was manufactured by forging. Next, each round bar was normalized under the conditions of heating and air cooling at 925°C for 1 hour, and then each normalized material was heated to 25 mm in diameter.
After turning, heating as shown in Table 1,
After being held at the soaking temperature for 1 hour, air cooling was performed. Next, from each treated material, a cylindrical V-grooved compression test piece 1 (D=14 mm, H
=21mm, θ=30°, d ₁ =0.8mm, R=0.15mm, α=
120°, d ₂ = 0.57 mm), and a compression test was performed using an Amsler testing machine with upper and lower end face constraint dies attached to simulate the production of mechanical structural parts by cold forging. Then, during the compression test, the deformability was evaluated using the compression ratio at which a crack occurred in the V-groove 1b as the crack generation limit. The results are spheroidized heat-treated carbon steel S40C and S48C (SA).
The results are also shown in Table 1.

[Table] As shown in Table 1, all steel types whose chemical composition falls within the scope of this invention develop a fine ferrite-pearlite structure by air cooling from the ferrite-austenite two-phase temperature range, and deformation exceeds that of S40C and S48C. showed ability. Also, the Si content is too high
No. 5 and No. 7, which had an excessively high Cr content, had lower deformability than this. Example 2 Next, among the steel types shown in Table 1, No. 1 (S40C),
Regarding No. 2 (S48C) and No. 3-5, 8-10,
After processing the normalized material under the same conditions as in Example 1 to a diameter of 25 mm, it was heated at the quenching temperature shown in Table 2 for 1 hour and then oil-cooled.
Steel No. 8 to No. 10 is tempered by heating to 170℃ for 1 hour and then air cooling, and No. 1 and No. 2 are tempered.
After tempering, which involves heating to 600°C for 1 hour and then rapidly cooling, hardness measurements, tensile tests, and impact tests were performed. At this time, the hardness was measured using a Rockwell C scale, the tensile test was performed using a JIS No. 4 test piece (reduced size), and the impact test was performed using a JIS No. 3 Sharpie test piece. These results are No.1
(S40C) and No. 2 (S48C) are shown in Table 2 together with the results of the tempered materials.

【table】

[Table] In this example, the quenching temperature is in the two-phase temperature range, so the quenching structure becomes fine ferrite-martensite or bainite.
Both impact values exceeded S40C and S48C tempered materials.
However, in No. 5 with Si exceeding 3%, the impact value was lower than that of S40C and S48C tempered materials. Example 3 Next, No. 8 to No. 10 steels according to the present invention shown in Table 1 were subjected to salt bath treatment in the ferrite-austenite two-phase temperature range shown in Table 3.
A compression test was carried out using the same test piece as in the case of , and the crack generation limit was measured. The results are also shown in Table 3.

[Table] As shown in Table 3, by the treatment in this example, the three steel types (N6 to 8) of this invention have a fine ferrite-bainite structure, which is equivalent to or higher than that of carbon steel SA-treated material. It showed deformability. Example 4 Next, for No. 4 and No. 10 steel round bars with diameters of 27.1 mm, 29.9 mm, and 32.3 mm according to the present invention shown in Table 1,
After rolling to a diameter of 25 mm at the rolling temperature and reduction ratio shown in Table 4, test pieces similar to those in Example 1 were prepared and subjected to a compression test to determine the limit of crack occurrence. The results are also shown in Table 4.

[Table] As shown in Table 4, when a reduction rate of 20% or more is applied in the temperature range of Ar ₁ transformation point to Ar ₃ transformation point + 100°C during finish rolling in material rolling, subsequent cold plastic working The crack occurrence limit becomes larger in
It was confirmed that cold plastic workability could be improved. (Effects of the Invention) As explained above, the method for manufacturing mechanical structural parts according to the present invention has C: 0.05 to 0.05 in weight%.
Less than 0.2%, Si: over 1.5 ~ 3%, Mn: over 1.0 ~
2%, Cr: 0.3 to 1.3% as a basic component, as necessary, one or two of Ni: 2% or less, Mo: 0.5% or less, Al: 0.1
% or less, Nb: 0.3% or less, Ta: 0.3% or less, Ti:
Contains one or more of the following: 0.3% or less, Zr: 0.1% or less, N: 0.03% or less, with the balance consisting of Fe and impurities, and is cooled by air cooling or higher from the ferrite-austenite two-phase temperature range. By cooling at a high speed, or by applying a reduction rate of at least 20% in the temperature range of Ar ₁ transformation point to Ar ₃ transformation point + 100℃ during finish rolling in material rolling prior to cold forging, or after applying air cooling or By performing cooling at a cooling rate higher than that, mechanical structural parts can be manufactured by cold forging using steel materials with microstructures of ferrite-pearlite, ferrite-pearlite-bainite, or ferrite-bainite. As a result, high deformability can be obtained during cold forging, and cold forging can be performed without performing spheroidizing heat treatment, which takes a long time and requires a huge amount of energy. It has extremely good deformability and excellent cold forging properties during
It is easy to manufacture various mechanical structural parts such as constant velocity joint parts such as outer races and housing shafts, and axle parts such as rear spindles and axle shafts by cold forging.
A very excellent effect can be obtained in that the scope of application of cold forging to various mechanical structural parts, which has high dimensional accuracy and good yield, can be significantly expanded.

[Brief explanation of drawings]

1, 2 and 3 are overall explanatory views of compression test pieces used in the examples of the present invention,
They are an enlarged explanatory view of a V groove part and an enlarged explanatory view of a center hole part.

Claims (1)

[Claims] 1% by weight: C: 0.05 to less than 0.2%, Si: more than 1.5 to 3%, Mn: more than 1.0 to 2%, Cr: 0.3 to 1.3%.
is the basic component, with the remainder consisting of Fe and impurities,
By cooling from the ferrite-austenite two-phase temperature range with air cooling or a cooling rate higher than that, fine ferrite-pearlite, ferrite-pearlite-
1. A method for manufacturing mechanical structural parts, characterized in that they are manufactured by cold forging using a steel material having a bainite or ferrite-bainite structure. 2 In weight%, C: 0.05 to less than 0.2%, Si: more than 1.5 to 3%, Mn: more than 1.0 to 2%, Cr: 03 to 1.3%
Contains one or two of the following: Ni: 2% or less, Mo: 0.5% or less, the balance is Fe and impurities, and the cooling rate is air cooling or higher from the ferrite-austenite two-phase temperature range. 1. A method for manufacturing mechanical structural parts, which comprises manufacturing by cold forging using a steel material having a fine ferrite-pearlite, ferrite-pearlite-bainite, or ferrite-bainite structure. 3 In weight%, C: 0.05 to less than 0.2%, Si: more than 1.5 to 3%, Mn: more than 1.0 to 2%, Cr: 0.3 to 1.3%
The basic components are Al: 0.1% or less, Nb: 0.3% or less, Ta: 0.3% or less, Ti: 0.3% or less, Zr: 0.1%
Hereinafter, N: Contains one or more of 0.03% or less, the balance is Fe and impurities, and is cooled from the ferrite-austenite two-phase temperature range by air cooling or a cooling rate higher than that, and fine ferrite- 1. A method for manufacturing mechanical structural parts, characterized in that the parts are manufactured by cold forging using a steel material having a pearlite, ferrite-pearlite-bainite, or ferrite-bainite structure. 4 In weight%, C: 0.05 to less than 0.2%, Si: more than 1.5 to 3%, Mn: more than 1.0 to 2%, Cr: 0.3 to 1.3%
are the basic components, Ni: 2% or less, Mo: 0.5% or less, one or two of them, Al: 0.1% or less,
One of the following: Nb: 0.3% or less, Ta: 0.3% or less, Ti: 0.3% or less, Zr: 0.1% or less, N: 0.03% or less
The balance consists of Fe and impurities, and is cooled from the ferrite-austenite two-phase temperature range with air cooling or a cooling rate higher than that to produce fine ferrite-pearlite, ferrite-pearlite-bainite, or ferrite- 1. A method for manufacturing mechanical structural parts, characterized in that the parts are manufactured by cold forging using a steel material having a bainite structure. 5 In weight%, C: 0.05 to less than 0.2%, Si: more than 1.5 to 3%, Mn: more than 1.0 to 2%, Cr: 0.3 to 1.3%
is the basic component, with the remainder consisting of Fe and impurities,
During finish rolling in material rolling prior to cold forging, a reduction rate of at least 20% is applied in the temperature range of Ar ₁ transformation point to Ar ₃ transformation point + 100 ° C, and then cooled with air cooling or a cooling rate higher than that, 1. A method for manufacturing mechanical structural parts, which comprises manufacturing by cold forging using a steel material having a fine ferrite-pearlite, ferrite-pearlite-bainite, or ferrite-bainite structure. 6 In weight%, C: 0.05 to less than 0.2%, Si: more than 1.5 to 3%, Mn: more than 1.0 to 2%, Cr: 0.3 to 1.3%
Contains one or two of the following: Ni: 2% or less, Mo: 0.5% or less, and the remainder consists of Fe and impurities, which undergoes Ar ₁ transformation during finish rolling in material rolling prior to cold forging. After applying a reduction rate of at least 20% in the temperature range from point to Ar ₃ transformation point + 100℃, cooling with air cooling or a higher cooling rate to form fine ferrite-pearlite, ferrite-pearlite-bainite, or ferrite- 1. A method for manufacturing mechanical structural parts, characterized in that the parts are manufactured by cold forging using a steel material having a bainite structure. 7 In weight%, C: 0.05 to less than 0.2%, Si: more than 1.5 to 3%, Mn: more than 1.0 to 2%, Cr: 0.3 to 1.3%
The basic components are Al: 0.1% or less, Nb: 0.3% or less, Ta: 0.3% or less, Ti: 0.3% or less, Zr: 0.1%
Contains one or more of the following: N: 0.03% or less, with the balance consisting of Fe and impurities, during finish rolling in material rolling prior to cold forging,
After applying a reduction rate of at least 20% in the temperature range of Ar ₁ transformation point to Ar ₃ transformation point + 100℃, cooling with air cooling or a cooling rate higher than that, fine ferrite-pearlite, ferrite-pearlite-bainite, Alternatively, a method for manufacturing mechanical structural parts, characterized in that they are manufactured by cold forging using a steel material having a ferrite-bainite structure. 8 Weight%: C: 0.05 to less than 0.2%, Si: more than 1.5 to 3%, Mn: more than 1.0 to 2%, Cr: 0.3 to 1.3%
are the basic components, Ni: 2% or less, Mo: 0.5% or less, one or two of them, Al: 0.1% or less,
One of the following: Nb: 0.3% or less, Ta: 0.3% or less, Ti: 0.3% or less, Zr: 0.1% or less, N: 0.03% or less
A reduction rate of at least 20% in the temperature range of Ar ₁ transformation point to Ar ₃ transformation point + 100°C during finish rolling in material rolling prior to cold forging. is added, then cooled with air cooling or a cooling rate higher than that, and manufactured by cold forging using a steel material having a fine ferrite-pearlite, ferrite-pearlite-bainite, or ferrite-bainite structure. A method for manufacturing mechanical structural parts.